1. Field of the Invention
The present invention relates to a diffusive reflector applied in a reflective LCD, and especially relates to the process and structure of a slanting diffusive reflector.
2. Related Art
A reflective LCD usually comprises an upper polarizer, a liquid crystal cell, a lower polarizer and a diffusive reflector. The liquid crystal cell consists of two parallel glass laminates and liquid crystal material filled in the space between the two glass laminates. Alignment layers and transparent electrode films are formed on the inner surfaces of the two glass laminates. Generally speaking, users view images from the LCD in an orthogonal direction and light is transmitted into the LCD in a non-orthogonal direction. For example, light is transmitted from somewhere above the LCD in a direction of twelve o""clock to the LCD. Light passes through the upper polarizer, the liquid crystal cell, the lower polarizer and is then reflected by the diffusive reflector, passing through the lower polarizer, the liquid crystal cell, the upper polarizer and finally becomes a signal light and observable by the human eye. How to design a good diffusive reflector with high light efficiency is an important issue in reflective LCD structure. How to increase the intensity of the light to be viewed and how to simplify the manufacturing process are important issues for manufacturing diffusive reflectors. The slanting diffusive reflector comprises an angle that enables incident light and signal light to have non-mirror image reflection so the signal light and glare generated by the glass laminate (or polarizer) can be separated and the incident light utilization rate is increased. Therefore, the quality of the reflective LCD is increased.
The conventional method of manufacturing slanting diffusive reflectors requires two different photo masks for two different light exposure processes. Usually, a photo resist on a substrate is exposed to form slants and then exposed again to form bumps for astigmatism on the slants. The traditional method requires two exposures so the manufacturing process is very complicated and the cost of production is very high. Therefore, it is necessary to provide a new manufacturing process and structure of slanting diffusive reflectors.
Accordingly, the object of the invention is to simplify the manufacturing process and reduce cost, so a new manufacturing process and structure of slanting diffusive reflector are proposed.
To obtain this object, a special photo resist is used in order to perform half-tone photolithography to a positive photoresist on a substrate. Only one photolithography process is required to form a slanting structure and bumps on the photo mask. The special photo mask comprises a plurality of half-tone exposure units. The size of the half-tone exposure units can be arranged arbitrarily. Each half-tone exposure unit comprises a plurality of parallel transmitting strips or shadow strips. The transmitting strips or shadow strips have suitable but arbitrary shapes. Arbitrary pitch can be obtained between the transmitting strips or the shadow strips in the same half-tone exposure unit. The width of the transmitting strip or the shadow strip can be increasing all the way from one side of the half-tone exposure unit to the other side (or decreasing in the opposite direction). As soon as the photo mask is used to perform out of focus exposure on the photoresist, the distance between the photoresist and focus is adjusted so the light penetrates the half-tone exposure units and generates zigzag light intensity (light intensity is changing from strong to weak or from weak to strong) distribution on the photoresist. After the above out of focus exposure process is performed, a suitable developing process and dry process are also performed to form a plurality of randomly sized bumps for astigmatism on the slants.
The manufacturing method of a slanting diffusive reflector comprises the following steps: provide a substrate upon which a positive photoresist is formed, for example, the photoresist can be PC403, PC409 or PC452; provide a photo mask that comprises a plurality of half-tone exposure units, each half-tone exposure unit comprises a plurality of parallel transmitting strips or shadow strips; arbitrary pitch can be obtained between the transmitting strips or the shadow strips in the same half-tone exposure unit and the widths of the shadow strips are gradually decreasing from one side to the other; the photo mask is used to form slants containing a plurality of bumps; finally, dry the photoresist. It is better if the size of the half-tone exposure unit, the pitch between the transmitting strips or the shadow strips and the gradually changing width of the transmitting strips or the shadow strips in the half-tone exposure unit are distributed arbitrarily within the range of a LCD pixel corresponding to the photo mask. This allows the slants on the photoresist to provide better astigmatic ability after combining the subsequent processes.
The process mentioned above for drying the photoresist involves solidifying the slants of the photoresist after they are developed. The photoresist flows when it is heated up before it is completely solidified, so the bumps on the slants become less distinguished and decrease the photoresist""s astigmatic ability. A better method for drying the photoresist comprises following steps: dry the photoresist at 100-150xc2x0 C. for 5-30 minutes, then hard bake at about 200xc2x0 C. for over one hour. In this case, the fluid behavior of the photoresist, which makes the bumps less prominent, is reduced.
Furthermore, the structure of the slanting diffusive reflector of the invention comprises a substrate, a photoresist formed on the substrate, a plurality of slants formed on the photoresist, and a plurality of bumps formed on each of the slants. The bumps for providing astigmatism can be ripples. The edge length of the slants can be about 10-40 micrometers. A better condition is to have randomly sized slants within the range of one pixel in order to provide better astigmatic ability. The pitch between ripples in different slants can also be randomly arranged.
Further scope of applicability of the invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.